Monolithic electrical transformer



Jan. 13, 1970 D. E. TEAFORD 3,489,931

MONOLITHIC ELECTRICAL TRANSFORMER Filed Aug. 50. 1968 FIG. 3. U if' V/Ai h R X KK L\ w19 4+ f l/// /L a,l 7

United States Patent O 3,489,931 MONOLITHIC ELECTRICAL TRANSFORMERDawson E. Teaford, Riverside, Calif., assignor to Bourns, Inc., acorporation of California Filed Aug. 30, 1968, Ser. No. 756,444 Int. Ci.Htllv 7/00 U.S. Cl. S10-8.1 4 Claims ABSTRACT 0F THE DISCLOSURE Anelectrical transformer comprising two sets of integral ceramicpiezoelectric elements with intercalated electrode means, laminated andunited into a monolithic structure during a ceramic greenware stage andfired `with application of opposite polarizing potentials during coolingthrough the Curie point, whereby upon piezoelectric excitation of afirst set of the elements as a primary and consequent physicaldeformation of the monolithic structure a set of potentials is generatedin the second set of elements as a secondary and which generatedpotentials are combined as by serial connection of elements. Appliedprimary potential is preferably of frequency equal to the naturalfrequency of the polycrystalline monolithic structure.

The piezoelectric effect, and various natural and synthetic crystallinesubstances having capability for exhibiting the effect, have beenextensively investigated and reported in the technical and scientificliterature. Therein it is noted that piezoelectric devices may be madefrom unit crystals, and from polycrystalline ceramic masses; and that inthe case of the latter, which may be either one or mixtures of severaltitanate and zirconate ceramic materials, the devices may be molded orformed to a desired shape and fired. Such ceramic piezoelectric deviceshave attained wide acceptance and usage, especially in the eld of largetransducers for converting electric wave energy to acoustic orultrasonic wave energy.

In U.S, Patent No. 3,378,704, there is disclosed a method and means forconsiderably augmenting or improving the transduction effected bypiezoelectric transducers of formed polycrystalline ceramic materials.Also, attainment of special and unique piezoelectric transductioneffects is taught in the noted patent, e.g., bending effects, Referencemay be had to the patent for details; and the disclosure of the patentis incorporated herein by reference, in the interest of brevity of thisdisclosure.

In the present invention, the bending effect, or the equivalent thereof,produced by electrical excitation of a monolithic mass comprisingpolycrystalline ceramic piezoelectric material one portion of which massis polarized oppositely to another portion, is used to effect electricwave transformation of the character yperformed by an ordinaryelectrical transformer. Production of oppositely polarized portions of aunitary or monolithic mass of the piezoelectric material is fullyexplained in the patent and prior art. As an example, physical bowing orbending of a long thin mass of the monolithic ceramic material, rst inone direction or sense and then oppositely, is accomplished byapplication of an A.C. potential or wave to two sets of superposed longplate-like electrodes which are suitably dispersed in the mass so as tobe insulated, each from the other. The present invention utilizes suchbending, or an analogous physical deformation of the mass containing theenergized electrodes or plates, to generate, across an additional set orpair (or groups of pairs) of electrodes also similarly dispersed in themonolithic mass, a second A C. potential. As is evident, the potentialcreated between the opposite faces of a laminar portion of the polarizedpiezoelectric mass can be added to like potentials created acrosssimilar laminar portions of the monolithic mass by suitably connectingelectrodes disposed between the laminar portions. Thus a secondary A C.potential may be produced which may bear any of several desiredrelationships of magnitude to that of the applied primary or excitationpotential, within obvious limitations imposed by the practicablephysical dimensions of the transducer, and with the advantage thatphase-displacement etfects such as are characteristic of ordinaryinductive transformers may be substantially eliminated.

The preceding general statements concerning the nature of the inventionmake it evident that it is a principal object of the invention toprovide improvements in a monolithic electric wave transducer.

Another principal object of the invention is to provide improvements inelectric wave transformers.

An additional object of the invention is to provide means for permittingselection of various electric wave transformation ratios in a monolithicpiezoelectric ceramic transformer.

Other objects and advantages of the invention will be hereinafter statedor made evident in the appended eleams or in the following descriptionof details of a presently preferred exemplary physical embodiment of theinvention which is illustrated in the accompanying drawings forming apart of this description and in which drawings:

FIGURE 1 is a pictorial View of an exemplary monolithic piezoelectricceramic transductor device according to the invention, to no particularscale;

FIGURE 2 is a diagram indicating schematically the electricalconnections of electrodes of the exemplary monolithic piezoelectricceramic transductor depicted in FIGURE 1, during a stage of manufactureduring which certain masses of polycrystalline material are brought torespective states of polarization;

FIGURE 3 is a diagram similar to that of FIGURE 2, showing an exemplaryarrangement of electrical connections for the electrodes of theexemplary transductor for operating the latter in one mode; and

FIGURES 4a, 4b and 4c are plan views of ceramic greenware members withapplied conductive elements, used in producing the monolithic device ofFIGURE 1, and showing a selected arrangement of electrodeconfigurations.

Referring rst to FIGURE l, there is `shown a transductor 10 which hasextending therefrom sets of terminal connections including, for example,wire terminals T1 and T2. The transductor, which in the specificexemplary form is a potential transformer, is comprised essentially of amonolithic mass of polycrystalline piezoelectric material and embeddedvery thin conductors or electrodes with electrical leads or connections.The monolithic mass is made by a plural-step procedure comprising:first, laminating or stacking greenware elements (which elements in theillustrated embodiment are thin rectangular sheet-like members ofpolycrystalline ceramic material and organic binder, each membergenerally bearing one or more films of conductive paint or other flatthin conductor); secondly, die-pressing the laminae under high pressureto consolidate or integrate the `several greenware elements andinterspersed conductor films into an integral mass; thirdly, firing theintegral mass, and providing accessible terminals for the electrodesformed by the fired conductive paint; and thereafter polarizingrespective portions of the ceramic material by cooling the portionsthrough a range of temperatures including the Curie point of the ceramicmaterial while selectively applying polarizing potentials of properpolarity and strength to pairs of the electrodes.

In general, the individual procedural steps are similar to thoseutilized in producing the transducer disclosed in U.S. Patent No.3,378,704, and the materials employed may be those indicated in thatpatent. However, other polycrystalline piezoelectric ceramic materialsand other binder materials may be used. For examples, U.S. Patents Nos.2,425,626; 2,966,719; 3,125,618 and 3,223,494 disclose other ceramicgreenware binders; and such piezoelectric compounds or compositions asImetallic titanates, zirconates and titanate-zirconates may be used.

S that the completed monolith will be so polarized as to cause differentphysical distortions of different portions thereof whereby to accomplishgeneration of an output potential or signal incident to application ofan input potential or signal, the laminae or thin strips of greenwareare selectively provided with conductive areas or films of specificareal configurations, as will be more fully explained hereinafter.

In the diagrammatic representations of FIGURES 2 and 3, there isindicated a plurality of thin strips or wafers a, b, c, d, e, f, g, h,j, k, m, n, 0, p, q and r disposed in stacked or superposed relation.The individual strips are very thin, preferably of the order of one milor less in thickness, and of `length and width dependent upon desiredcharacteristics of the device; for example resonant frequency,transduction ratio, etc. For example, the strips may be 0.4 inch wideand two inches long. As is made evident in the drawings, the strips orgreenware lwafers are shown exaggerated in dimension in FIGURES 2 and 3,in the interest of clarity of detail. For convenience, the two oppositedirections of polarization utilized will be termed left and right,respectively; and the direction of polarization of the material in anyselected one of the strip-like elements is indicated in FIGURES 2 and 3by the direction of hatch marks, it being understood that polarizationis not accomplished until the strips are consolidated into an integralmonolithic structure. For example, strip a is indicated as being anelement or lamina to be polarized left, by the left-inclined hatchmarks; and step b as an element to be oppositely or right polarized, bythe right-leaning hatch marks. As indicated in the drawing, strip a isleft-polarized by application of negative potential over the uppersurface and positive potential over the lower surface; and strip b isoppositely polarized by application of opposite polarities of potential,as will presently be made more clearly evident.

In the diagrammatic representations of FIGURES 2 and 3, conductive filmsor electrodes which initially are deposited or formed on one or bothsides of a ceramic greenware strip, are for convenience and clarityshown merely as lines disposed between ceramic strips. Thus theelectrode a', shown disposed between strip a and an insulator strip z,is preferably initially formed on strip a; and similarly, conductiveelement or electrode b is preferably initially formed on strip b, and soon. As will be noted, in the exemplary transductor 10, the piezoelectric ceramic material in strips a, c, e, g, j, m, n, and o is tobecome polarized left, while that comprised in the remainder of thestrips is to be oppositely polarized, that is right This exemplaryillustration of selective polarization is such that the desired resultis attained, but as will be evident from consideration of electricalconnections, etc., in the nished product, other polarizationarrangements are possible. For an example, the polarization of piezoelements m, n and o, may be opposite to that shown, if the polarizationof elements p, q and r is similarly made opposite, or if appropriatechanges in electrical connections are made in the device. Thearrangement shown is merely illustrative.

To permit of selective polarization of the piezo elements or laminaefollowing formation of the monolithic ceramic structure, provisions aremade for application of electrical potentials across the elements asthey cool to a temperature below the Curie point. To that end, and topermit integration of the elements into a monolithic structure, theconductive or potentially-conductive paint or ink is applied to certainportions only of the face areas of the strips. Thus on the ceramicgreenware strips a and c (FIG- URE 4a) the conductive ink is appliedover the interior area A spaced inwardly from the edges sufficiently farto provide for adequate bonding of the strips into an integral ormonolithic structure, but as indicated is extended to the edge at aselected place to provide a termination t. On others of the strips, suchas for example strips b and d (FIGURE 4b) the conductive element issimilarly applied but so as to have a terminal t at a differentlocation, as indicated. In those instances in which integration orbonding of the material of the strip at the margins is insuicient toprovide desired integrity of the monolith, the conductive coating orfilm may be omitted from one or more small interior areas, such as thatindicated at y in FIGURES 4a and 4b.

As is made evident in FIGURES 2 and 3, certain of the greenware stripsmay bear a conductive ink coat or electrode pattern on both faces; forexample, note strips e, m and r. Since the several strips will be unitedinto an integral monolithic structure by compression in a closed die andby firing, the conductive paint or lm may be applied asmay be found tobe expedient, that is, on both sides of some strips and none on others,or otherwise, it being essential only that properly located terminals beprovided for and that a conductive electrode be disposed between eachpair of strips. The arrangement shown is exemplary only. The electrodesmay be formed by application of a platinate ink which is reduced to aplatinum film when the monolith is fired.

In the device illustrated, the primary strips are divided into two sets,an upper set comprising strips a through e, and a lower set comprisingstrips f, g, h, j and k. The set of secondary strips m, n, o, p, q andr, is disposed as indicated, between the primary sets. As willhereinafter be made evident each of the set of primary elements and theset of secondary elements may be considered to comprise upper and lowersubsets of elements. To insulate the exposed or adjacently disposedelectrodes, insulator strips z', are disposed as indicated in FIGURE 2.The insulator strips may be merely plain ceramic greenware strips notcarrying conductive paint, and may be of the same material as the otherstrips or may be of unlike but compatible material containing no piezomaterial. It is essential only that mutual bonding of the insulatorstrips with other strips be effective, and that the temperaturecoefficient of expansion be suiciently alike to avoid adverse effects oftemperature changes.

It will be understood that a termination tab or member such as t and t',but differently located, is provided for each of the conductiveelectrodes, and that the locations of the terminations are selected soas to facilitate electrical interconnection of appropriate electrodes sothat polarizing potentials may be applied and so that followingpolarization, sets of electrodes may be appropriately connected t0external circuits, all as will be made evident in the followingdescription of such connections.

Following die-pressing and firing of the consolidated elements, andapplication of terminal leads in a manner taught in U.S. Patent No.3,378,704, connections for polarization of inter-electrode zones orportions of the polycrystalline piezo material are made as indicated inFIGURE 2. Thus for that step of the procedure, electrodes a', c and eare by a conductor K connected to the low-potential side of a potentialdivider R at termial U (here indicated as the side). Similarly,electrodes b', d, and e" are by a conductor L connected to the oppositeside of the potential divider R at termial X. The latter is connectedacross a source of potential as indicated, of the order of severalhundred volts. As is evident, the polarity of the connections attermials U and X may be the reverse of that shown.

By means of other conductors, electrodes m and r are connected toterminal U of the divider, electrodes m and q are connected to taptermial V, electrodes n', p', f', h and k' to tap terminal W, andelectrodes g', j and k" are connected to termial X, all as indicated inFIG- URE 2. Thus, following application of terminals and heating of thedevice, as the monolithic mass and embedded electrodes cool through andto a temperature below the Curie point of the piezo material, theseveral inter-electrode portions of the material will be polarized asindicated, the left polarized portions being those indicated `byleft-slanting hatch marks, and the right polarized being the remainder,indicated by right-inclined hatching.

Following polarization of the several inter-electrode portions of thepolycrystalline monolithic mass as described, the electrode terminalconnections are disconnected and reconnected as indicated in FIGURE 3.For convenience in comparison and for clarity, the gross distortions indimension of FIGURE 2 are retained in FIGURE 3, but it will beunderstood that at this stage of manufacture the exemplary transductorwill be in general be a long thin device such as is shown in FIGURE l.With the electrodes reconnected as indicated in FIG- URE 3, applicationof alternating potential across ter minals T1' and T2 induces,alternately, longitudinal expansion and contraction forces in the zoneincluding the upper set of elements a, b, c, d, and e, with concurrentand opposite longitudinal contraction and expansion forces in the lowerset of elements f, g, h, j and k, whereby the entire structure bends orbows alternately in opposite directions. That is, when contractionforces are generated in the upper set of elements a, b, c, d and e,there are expansion forces simultaneously generated in elements f, g, h,j and k; and vice versa. Thus the device is caused to bend or vibrate atthe frequency of the applied A.C. potential.

Concurrently with the alternate bending in opposite directions of theouter groups of piezo elements, the inner subsets of elements m, n, o,and p, q, r, are vibrated synchronously with the remainder of themonolithic mass. The physical bending of piezo elements of the innersubsets generates potentials between the embedded secondary electrodesSince the upper subset of three elements m, n and o is disposed abovethe longitudinal center or axis of symmetry and the lower subset ofthree elements p, q and r is disposed below that axis, compressionforces exist in either when expansion (tension) forces exist in theother. However, due to the opposite polarization of the two subsets, thegenerated potentials are additive. Thus the sum of the generatedpotentials appears across electrodes m" and r and is made available atterminals T3 and T4 by means of the connections shown. The phaserelationship of the generated output potential to the driving potentialis dependent upon the arrangement of the interconnections of electrodes.

As is evident, parallel connection of electrodes of the two middlesubsets of elements may be elfected, as in the case of electrical cellsand other electric generators. Similarly, as is evident fromconsideration of the preceding descriptions, the middle portion of thedevice may be made to be the driver portion or primary by suitableconnections of the electrodes therein to a source of A.C. power orsignal input, and the upper and lower portions then used as thesecondary or output section of the device. As is also evident, input andoutput potential ratio may be selected by utilizing the required numbersof electrodes in the primary and secondary sets.

In the preceding description it has been lmade evident that electrodeplacement may be various, that is, electrode material may be applied toboth sides of some greenware strips, other strips being left uncoated;and that terminations are appropriately distributed along marginal edgesbut positioned to facilitate external connection of electrodes withnecessary spacing for inter-electrode insulation. As an example of agreenware strip bearing an electrode film on both faces, the strip e isshown in FIGURE 4c with electrode e on the visible or front face andelectrode e" of the same area on the back face. Electrode e has atermination at the left end of the strip, as indicated, whereby thepreviously described connections can be effected, Further, while thegreenware strips depicted on a grossly distorted scale and with portionsbroken out in FIGURES 2 and 3 are of simple rectangular shape, they maybe of other shapes and the device as a whole may be of other shape andof other than Hat form, as is made evident by review of theaforementioned Patent No. 3,378,704. Also, the arrangement of sets andsubsets of primary and secondary piezo elements may be other than asshown, subject only to being such that mechanical expansion andcontraction is effected by the driving set or primary and such as toeffect similar expansion and contraction of the secondary or driven set,and subject to the relative polarizations and electrode connectionsbeing effective to produce the described result.

In the light of the preceding description of an exemplary embodiment ofthe invention, changes will occur to others; and accordingly it is notdesired that the invention be restricted to the disclosed example otherthan as de.- lined in the appended claims.

I claim:

1. A piezoelectric transduction device comprising:

rst means, consisting essentially of a thin monolithic polycrystallineceramic mass,

second means, including a primary set and a secondary set of thinilmlike electrode elements embedded in said mass in closely-spacedlaminar relation with a respective thin polarized laminar piezoelectricportion of said ceramic mass interposed between next-adjacent ones ofsaid electrodes, said second means comprising a respective terminal foreach of said electrode elements, said thin electrode elements comprisinga primary set thereof and a secondary set thereof,

secondary electrical connections to electrodes of said secondary set ofelectrodes, and primary electrical connections to said primary setconnected to receive applied alternating potential to act to cause thepiezoelectric portions therebetween to act as a driver to alternatelydeform said ceramic mass in opposite directions,

said laminar portions disposed between electrodes of said primary setbeing so polarized relative to the potentials applied therecross as tocause physical deformation of said mass, and those laminar portionsdisposed between electrodes of said secondary set being polarized togenerate potentials therebetween incident to deformation of said ceramicmass, whereby upon application of alternating potential across saidprimary electrodes by way of said primary electrical connections saidmass alternately deforms in opposite directions and deforms the laminarportions between the electrodes of said secondary set whereby there isgenerated across electrodes of said secondary set respective alternatingpotentials.

2. A piezoelectric transductor device as defined in claim 1, in whichsaid ceramic mass is of long rectangular plan form and in whichdisposition and electrical connection of electrodes of said primary setis such as to cause 7 8 longitudinal bending of said mass, and in whichat least References Cited approximately equal numbers of primaryelectrode ele- UNITED STATES PATENTS ments are disposed on oppositesides of a longitudinal capacitor electrodes.

4. A piezoelectric transductor device according to claim J D MILLER,Pllmafy EXamme-r 1, in which the electrode elements of one of said sets10 Us C1 XR are disposed between rst and second subsets of the elec- 3108 2 9 5 9 7 trode elements of the other of said sets. f i

